past tense - Why “can” not “could” in “She was one of those people who can. . . .”?

The following sentence is from George Orwell’s Nineteen Eighty-Four, occurring in chapter 5 of part 2:

She was one of those people who can go to sleep at any hour and in any position.

Why is who can grammatically correct when used with was? Shouldn’t it be who could?

Answer

The description is taken from a novel; in that context, it is usual to refer to people using the past tense.

Who could relates not to the character just mentioned, but to the generic referent one of those people, whose characteristics can be described both by who can and who could.